To study effects of irrigation water and nitrogen fertilizer levels on grain yield and its components of maize (cv. SC704) and to evaluate economic efficiency of experimental treatments a filed experiment was carried out as split plot arrangement in randomized complete block design in 2014 and 2015 growing seasons at experimental field of Agriculture and Natural Resources Campus, Razi University, Kermanshah, Iran. Four irrigation water levels (60, 80, 100 and 120% of maize water requirement) were assigned to main plots, and four nitrogen fertilizer levels (40, 70, 100 and 140% of recommended levels based on soil test) were randomized in sub-plots. Results showed that regardless of nitrogen fertilizer levels, application of 120% of the maize water requirement, 8760 kg.ha-1 grain was produced and with reducing water requirements to 20, 40 and 60%, grain yield decreased by 10, 37 and 65%, respectively. Irrigation water and nitrogen supply simultaneously increased the total dry weight, grain yield and grain protein. At lower levels of irrigation water, there was no significant difference in grain yield between nitrogen fertilizer levels. However, application of 100 and 120% of the maize water requirement, nitrogen fertilizer up to recommended levels increased grain yield by its affect on ear size and yield components. Therefore, by application of 120% of maize water requirement and 100 and 140% of nitrogen requirement, 9340 and 9280 kg.ha-1 maize grain yield was achieved. Grain yield in these nitrogen levels and 100% of maize water requirement were 8770 and 8300 kg.ha-1. The highest gross and net return per hectare (82.94 and 48.99 million Rials in 2014 and 86.70 and 45.04 million Rials in 2015, respectively) were obtained by application of 120% of maize water requirement and 100% of nitrogen requirement. Optimum level of water economic efficiency (4200 and 3670 Rials.m3 in 2014 and 2015) and nitrogen (71060 and 48650 Rials.kg-1 in 2014 and 2015) were obtained by application of 100% of maize water requirement. The results also showed that with increasing nitrogen fertilizer application, economic efficiency of nitrogen decreased and nitrogen application up to 70% of recommended level improved economic efficiency of maize. Although the highest grain yield and net income were obtained by application of 120% of maize water requirement and 100% of nitrogen requirement, but appropriate combination of irrigation water and nitrogen levels is recommended considering the importance, price changes, economic productivity and environmental constraints of each inputs.